you could build it yourself. its not hard. people just feel intimidated by it. you will get more bang for your buck. if you spend $600 on a pc at the store, by comparison that same 600 for your to build it will get you a way better system.
i would say 600 would be your minimum amount.
you will need
CPU - $229 (extremely popular)
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115072&Tpk=i5 2500k
Motherboard - 114 (this is what i have)
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130583
Power Supply (at least 650w) $89 you really dont want to skimp on a psu. you want a quality device
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139020
Ram (at least 4 gb) $25
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231425
Graphics Card $270 this is the card i have...its fucking awesome! your gonna need to shop around and decide what is in your budget
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127608
Case $60 you can go even cheaper here depending on what you care about
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119233
Dvd Burner $20 how can u go wrong...i have this one
http://www.newegg.com/Product/Product.aspx?Item=N82E16827135204
Hard Drive- Hard drive costs have gone up because they are made in thailand and they had the floods. prices doubled after that. expect to spend $100
CPU Fan (Stock fan that comes with it suck) $30 2500 people cant be wrong. i have this one. your processor will come with a fan. you can use that but under load they are pretty crappy. most people elect for an aftermarket fan
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103065
Windows 7 - $100 alot of people forget about this. you need an OS and dont think about linux because all games need windows to run
[ame="http://www.amazon.com/gp/product/B004Q0PT3I/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B004Q0PTD8&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0V1VFMP54RCM5Z60V7PZ"]Amazon.com: Windows 7 Home Premium SP1 64bit (Full) System Builder DVD 1 Pack: Software[/ame]
FYI i own that exact version of windows. it can be used multiple times on your pc. According to MS, it can be installed by the builder on any PC. the catch is you dont have any support from MS
your about $950 right there. that would be a tits PC. you could probably shed anywhere from 100-300 off the cost with a lower cpu, psu, case and graphics card and bargains from newegg
bottom line...u want to be a pc gamer your gonna pay the price. is it worth it? when i make a post like this i begin to wonder. then i look over at my big ass case with its red light staring back at me and i think about how i can overclock the cpu, gpu and ram or add more hdd or another ssd or blue ray burner and then i think...fuck yeah it was totally worth it
sidenote....do your own research and decide for yourself what to buy. Designing the PC you want is 90% of the fun of doing it